The present invention relates to projection type image display apparatuses, and particularly relates to a technique preventing scintillation by moving a screen of the projection type image display apparatus.
A general projection type image display apparatus such as a rear-projection type television includes a lamp as a light source. Recently, it has been developed to use a laser or the like as the light source, in order to enhance image quality and brightness.
It is known that, when the laser is used as the light source, a speckle pattern is caused by interference of laser lights diffused by a screen. Such a speckle pattern is observed as flicker on the screen. This phenomenon is called as scintillation.
In order to reduce scintillation, there is proposed a method of vibrating the screen in a direction perpendicular to an emitting surface (i.e., a display surface) of the screen, a longitudinal direction of the screen, or a widthwise direction of the screen (see, for example, Patent Document No. 1).
However, when the screen is vibrated in the direction perpendicular to the emitting surface, the display surface is shifted frontward or rearward with respect to a focal position of a projection optical system, and therefore image resolution may be degraded.
Further, when the screen is vibrated in the longitudinal direction or widthwise direction of the screen, the screen moves intermittently (i.e., repeatedly moves and stops). Therefore, a state where strong scintillation is observed (when the screen stops) and a state where substantially no scintillation is observed (when the screen moves) are repeated. In other words, the scintillation becomes alternately stronger and weaker.
Therefore, there is proposed a technique of reducing the scintillation, in which a lenticular lens screen (i.e., a component of the screen) is supported using a resilient body such as a rubber, and the lenticular lens screen is circularly moved in a plane parallel to an emitting surface thereof (see, for example, Patent Document Nos. 2, 3 and 4).    Patent Document No. 1: Japanese Laid-open Patent Publication No. S55-65940 (Pages 4-6, FIGS. 1-2)    Patent Document No. 2: Japanese Laid-open Patent Publication No. 2007-298945 (Pages 5-7, FIG. 2)    Patent Document No. 3: Japanese Laid-open Patent Publication No. 2007-286346 (Page 8, FIG. 4)    Patent Document No. 4: Japanese Laid-open Patent Publication No. 2007-328002 (Page 7, FIG. 5)
In a configuration in which the component (i.e., the lenticular lens screen) of the screen is circularly moved, it is necessary to provide a motor or the like generating a large torque for circularly moving the component of the screen. Therefore, it becomes difficult to reduce size and weight of the projection type image display apparatus. Further, in a configuration in which the component of the screen is held by the resilient body such as rubber, it is difficult to stably support the circular movement of the component.